German patent application 10 2014 115 577.7 which has not yet been published discloses a controllable shock absorber for a motor vehicle chassis. A pilot control pressure for loading the valve plates by means of a magnet actuator can be set in a targeted manner via a valve assembly. Here, the pilot control pressure is set both in the compression stage and in the rebound stage with the aid of a valve body. During regular operation, the fluid which flows out via the pilot control valve is guided via a first outflow path, in which an outflow valve with comparatively soft characteristics is provided. For the case where the magnet actuator fails and therefore the actuation of the pilot control valve fails, the fluid is conducted through a second outflow path, in which a failsafe valve with a comparatively hard characteristic is arranged, and by way of which failsafe valve emergency running properties are set. The switchover of the outflow path takes place by way of the valve body itself; if the magnet actuator fails, the valve body is automatically moved into a position, in which it shuts an inlet opening of the first outflow path.
It is fundamentally preferred in shock absorbers of this type if the damping characteristic of the shock absorber can be set in the individual stages (compression stage, movement of the piston in the direction of the working space which is remote from the piston rod, and rebound stage, movement of the piston in the direction of the piston rod-side working space) as far as possible independently of the respective other stage.
One particular possibility of an individual setting capability of this type is disclosed in DE 10 2011 000 566 B3. A shock absorber with a controllable pilot control means is described here, in which shock absorber the active faces on the pilot control valve are configured differently for the two stages. Different loading of the valve body during the individual stages is thus generated. This has not been able to be applied up to now, however, to valve bodies of the type, by way of which the switchover between two outflow parts is also to be realized. This is because the valve body is loaded directly by the working pressure in the working space which is remote from the piston rod in the compression stage. Above a certain piston speed, the valve body is opened completely and is transferred into its upper stop position. If, however, the valve body is then at the same time also to take on the switchover to the failsafe function, the regular (first) outflow path is at the same time also shut by way of the stop position, and the (second) outflow path is activated via the failsafe valve.
Thus a need exists for an improved controllable shock absorber and in the process, in particular, an improved and universally applicable possibility for the individual setting capability of the damping characteristic for the individual stages.